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Equine internal parasites

All horses have internal parasites. Many instances of colic may be related to blood vessels damage caused by the migrating larvae of Strongylus valgaris (blood worms). A high percentage of deaths amongst horses may be related to internal parasites.

Internal parasites have adapted themselves to the internal environment of their host animal and have become host-specific. Horse parasites can only exist in horses. This can be a useful factor when considering parasite control.

Major Parasites
There are five major kinds of equine internal parasites: large and small strongyles, ascarids, bots, and pinworms.

Large and Small Strongyles
The most common and most destructive of all internal equine parasites in the horse are the large strongyles. Strongyles can be seen in horses of all ages, except in very young foals. Strongyles range in length from 1/2 inch to 2 inches.

Ascarids
Parascaris equorum (large roundworms) are the largest internal parasite affecting the horse, ranging from 5inches to 15inches long. Ascarids reach up to 1/2 inch in diameter when mature and look like round earth worms. These parasites are common in young horses and are not always found in horses over five years old. Immunity normally develops following exposure to these large roundworms during adolescence.

Bots
Bots come in three types: Gastrophilus intestinalis, which is the most common; Gastrophilus haemorrhoidalis, the nose bot; and Gastrophilus nasalis the throat bot.

Pinworms
Oxyuris equi (pinworm) are found in the cecum, colon, large intestine, and rectum. Female worms are normally full of eggs which pass out in the faeces. Female pinworms also crawl out of the anal opening and deposit their eggs on the surrounding skin, causing irritation and itching.

Internal parasite control is a continual battle and there are some obvious Stable Management routines that can help:

1 Regular cleaning of stables and paddocks
2 Feeding hay in mangers and nets.
3 Do not spread manure were horses can come into contact with it.
4 Avoid when possible wet pastures- rain, dew, flooding, especially with young animals.
5 Working droppings loose with a harrow, or disk to bury manure and destroy weed growth.
6 If possible the grazing of cattle in horse pastures decreases exposure as equine parasites do not mature in cattle and the parasites life cycle is broken.

The proper treatment program using the right wormers at the right time is essential for good control. There are many excellent wormers sold under brand names with the three main active chemicals in wormers purchased in the UK are Ivormectim, Mebendazole and Pyrantel Embonate. There are other chemicals but a good program can be established with the above. It is not always appreciated that these chemicals cause various degrees of short-term toxic shock and it is important to get your horse over these effects as quickly as possible.

This article was kindly provided by Trinity Consultants

Trinity Consultants recognise the important need to worm horses correctly with the correct chemical, at the correct time and the correct dose. To help you we now run a comprehensive worming register for our clients. If you would like to join the worming register or learn more about internal parasites, their life cycle and their effects upon the horse please contact Trinity Consultants. Phone or mail.willjer@itl.net Trinity Consultants on +44 (0) 1243 551766 fax +44 (0) 1243 55622 or in Jersey on +44 (0) 1543 863495.